[PATCH v3] locking/spinlocks, paravirt, hyperv: Correct the hv_nopvspin case

[PATCH v3] locking/spinlocks, paravirt, hyperv: Correct the hv_nopvspin case

[Zhenzhong Duan]

With the boot parameter "hv_nopvspin" specified a Hyperv guest should
not make use of paravirt spinlocks, but behave as if running on bare
metal. This is not true, however, as the qspinlock code will fall back
to a test-and-set scheme when it is detecting a hypervisor.

In order to avoid this disable the virt_spin_lock_key.

Same change for XEN is already in Commit e6fd28eb3522
("locking/spinlocks, paravirt, xen: Correct the xen_nopvspin case")

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Cc: Sasha Levin <sashal@kernel.org>
Cc: Juergen Gross <jgross@suse.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: linux-hyperv@vger.kernel.org
---
v3: remove unlikely() as suggested by Sasha

 arch/x86/hyperv/hv_spinlock.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/hyperv/hv_spinlock.c b/arch/x86/hyperv/hv_spinlock.c
index 07f21a0..210495b 100644
--- a/arch/x86/hyperv/hv_spinlock.c
+++ b/arch/x86/hyperv/hv_spinlock.c
@@ -64,6 +64,9 @@ __visible bool hv_vcpu_is_preempted(int vcpu)
 
 void __init hv_init_spinlocks(void)
 {
+	if (!hv_pvspin)
+		static_branch_disable(&virt_spin_lock_key);
+
 	if (!hv_pvspin || !apic ||
 	    !(ms_hyperv.hints & HV_X64_CLUSTER_IPI_RECOMMENDED) ||
 	    !(ms_hyperv.features & HV_X64_MSR_GUEST_IDLE_AVAILABLE)) {
-- 
1.8.3.1

Re: [PATCH v3] locking/spinlocks, paravirt, hyperv: Correct the hv_nopvspin case

[Zhenzhong Duan]

Hi Maintainers,

Any further comments on this? Thanks

Zhenzhong

On 2019/7/3 10:23, Zhenzhong Duan wrote:
> With the boot parameter "hv_nopvspin" specified a Hyperv guest should
> not make use of paravirt spinlocks, but behave as if running on bare
> metal. This is not true, however, as the qspinlock code will fall back
> to a test-and-set scheme when it is detecting a hypervisor.
>
> In order to avoid this disable the virt_spin_lock_key.
>
> Same change for XEN is already in Commit e6fd28eb3522
> ("locking/spinlocks, paravirt, xen: Correct the xen_nopvspin case")
>
> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
> Cc: "K. Y. Srinivasan" <kys@microsoft.com>
> Cc: Haiyang Zhang <haiyangz@microsoft.com>
> Cc: Stephen Hemminger <sthemmin@microsoft.com>
> Cc: Sasha Levin <sashal@kernel.org>
> Cc: Juergen Gross <jgross@suse.com>
> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Waiman Long <longman@redhat.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: linux-hyperv@vger.kernel.org
> ---
> v3: remove unlikely() as suggested by Sasha
>
>   arch/x86/hyperv/hv_spinlock.c | 3 +++
>   1 file changed, 3 insertions(+)
>
> diff --git a/arch/x86/hyperv/hv_spinlock.c b/arch/x86/hyperv/hv_spinlock.c
> index 07f21a0..210495b 100644
> --- a/arch/x86/hyperv/hv_spinlock.c
> +++ b/arch/x86/hyperv/hv_spinlock.c
> @@ -64,6 +64,9 @@ __visible bool hv_vcpu_is_preempted(int vcpu)
>   
>   void __init hv_init_spinlocks(void)
>   {
> +	if (!hv_pvspin)
> +		static_branch_disable(&virt_spin_lock_key);
> +
>   	if (!hv_pvspin || !apic ||
>   	    !(ms_hyperv.hints & HV_X64_CLUSTER_IPI_RECOMMENDED) ||
>   	    !(ms_hyperv.features & HV_X64_MSR_GUEST_IDLE_AVAILABLE)) {